The neurotensin-1 receptor agonist PD149163 inhibitsconditioned avoidance responding without producing catalepsyin rats

Elizabeth N. Holly, Bree Ebrecht, and Adam J. Prus*

AbstractAgonists for neurotensin (NT)-1 receptors have produced antipsychotic-like effects in manyanimals, including reversal of prepulse inhibition deficits and psychostimulant-induced increasesin spontaneous activity. The present study sought to provide a basic assessment of the putativeantipsychotic effects of PD149163 in rats using a two way conditioned avoidance response task,which is highly validated for screening antipsychotic drugs, and an inclined grid assessment,which is used to assess extrapyramidal side effect liability. PD149163 (0.0625-8.0 mg/kg)significantly suppressed conditioned avoidance responding (CAR) following administration of a1.0 or 8.0 mg/kg dose. PD149163 failed to significantly increase catalepsy scores. The typicalantipsychotic drug haloperidol (0.01 – 1.0 mg/kg) significantly suppressed CAR at a 0.1, 0.3, and1.0 mg/kg dose, and a significant increase in catalepsy scores was found at the 1.0 mg/kg dose.The atypical antipsychotic drug clozapine (2.5-10.0 mg/kg) also produced a significant inhibitionof CAR, which occurred following administration of a 10.0 mg/kg dose. Clozapine failed tosignificantly increase catalepsy scores. Finally, d-amphetamine (1.0 mg/kg), serving as a negativecontrol, failed to suppress CAR or increase catalepsy scores. These data further suggest thatPD149163 may have atypical antipsychotic-like properties.

KeywordsPD149163; neurotensin; haloperidol; clozapine; conditioned avoidance response; catalepsy

1. IntroductionPD149163 is a brain penetrant neurotensin (NT)1 receptor agonist (Petrie et al. 2004;Wustrow et al. 1995) that has been studied for several years as a putative atypicalantipsychotic drug (APD). While the definition of an atypical APD has varied over the pastseveral decades, due to different pharmacologic hypotheses (e.g., 5-HT2A/D2, D2 “fast-off”,D2 receptor partial agonism) and differences in treatment efficacy (e.g., negative symptom

*Corresponding author: Adam Prus, Ph.D., Associate Professor, Psychology Department, Northern Michigan University, 1401 PresqueIsle Ave., Marquette, Michigan, USA 49855, Phone: 1-906-227-2941, Fax: 1-906-227-2954, aprus@nmu.edu.Contributors: Elizabeth Holly and Bree Ebrecht both conducted data collection, managed literature searches, and contributed writingto the first draft of this manuscript for this study. Dr. Adam Prus designed and supervised the study, conducted the statistical analyses,and completed the final draft of this manuscript.Conflict of Interest: Dr. Adam Prus received an NIMH grant (1R15MH083241-01) to study the effects of neurotensin receptoragonists for the treatment of schizophrenia. All other authors declare that they have no conflicts of interest.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to ourcustomers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review ofthe resulting proof before it is published in its final citable form. Please note that during the production process errors may bediscovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

NIH Public AccessAuthor ManuscriptEur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

Published in final edited form as:Eur Neuropsychopharmacol. 2011 July ; 21(7): 526–531. doi:10.1016/j.euroneuro.2010.12.004.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

and cognitive efficacy), a basic requirement remains an ability to reduce positive symptomsin schizophrenia without producing extrapyramidal side effects (EPS) at therapeuticallyeffective doses (Gerlach 2002; Goldstein 2000).

These basic atypical APD properties have been thoroughly evaluated for many NT1 receptoragonists. PD149163 (Feifel et al. 2008), as well as the NT1 receptor agonists NT69L (Bouleset al. 2001; Cusack et al. 2000), NT79 (Boules et al. 2010), and KH28 (Hadden et al. 2005)have reduced psychostimulant-induced increases in locomotion and other stereotypicbehaviors in rodents, a common screen for APD effects. Moreover, PD149163 (Feifel et al.2004), NT69L (Cusack et al. 2000), and KH28 (Hadden et al. 2005) have not been shown toexhibit catalepsy in rats, similar to the atypical APD clozapine, but not the typical APDhaloperidol (Feifel et al. 2004). NT69L (Shilling et al. 2003), NT79 (Boules et al. 2010), andPD149163 (Feifel et al. 2008; Feifel et al. 2003; Feifel et al. 1999), also have been shown toprevent prepulse inhibition deficits produced by various psychotomimetic drugs, whichmight predict their efficacy for sensory gating deficits in schizophrenia.

The conditioned avoidance response task is another standard method for behaviorallyscreening putative APDs and offers few false positive results (Wadenberg and Hicks 1999).In this task, animals, usually rats, are trained to avoid a floor grid shock when a warningstimulus, usually a tone or white noise, is activated. APD effects are represented asdecreases in avoidance responses without failures to escape the foot shock. Atypicality maybe inferred by an additional assessment of catalepsy at doses that produce decreases inavoidance responding. Intracerebroventricular injection of NT has produced decreases inconditioned avoidance responding (CAR) without producing escape failures in rats(Luttinger et al. 1982), although catalepsy has been reported in mice (Adams et al. 1997;Shibata et al. 1987; Snijders et al. 1982). Systemic administration of NT69L has been shownto inhibit CAR (Hertel et al. 2002) at doses that have not produced catalepsy in rats (Cusacket al. 2000; Sarhan et al. 1997).

While PD149163 has been thoroughly characterized in other APD models, only one report isavailable for the lack of cataleptic effects (Feifel et al. 2004). Moreover, there are nopublished studies on the effects of PD149163 on CAR. Thus, the present study wasconducted to further evaluate the APD effects of PD149163 using the conditioned avoidanceresponse task, which is highly predictive of APD effects, and using an inclined grip task toassess catalepsy, an indication of EPS liability. The effects of PD149163 were compared tothe atypical APD clozapine and the typical APD haloperidol in both procedures. Finally, D-amphetamine was tested as a negative control.

2. Experimental Procedures2.1 Subjects

Ten male Sprague Dawley rats (Charles River, Portage, MI, USA) were used for allexperiments. Animals were housed two per cage under stable laboratory conditions(21±2°C, 55±5% relative humidity) under a 12 hour light/dark cycle (lights on at 07:00am).All experiments were conducted at approximately the same time each day. Food and waterwas available ad libitum in the home cages. All procedures were approved by the NorthernMichigan University Institutional Animal Care and Use Committee and performed incompliance with the Guide for the Care and Use of Laboratory Animals (National ResearchCouncil 1996).

2.2 ApparatusTwo shuttlebox test chambers equipped with a tilting shock grid floor and white noisespeakers in each compartment were used for these procedures (Med Associates Inc., St.

Holly et al. Page 2

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Albans, VT, USA). The box was housed in a sound attenuating chamber equipped with aventilation fan and masking noise. Data were collected using MedPC IV software (MedAssociates Inc.). Catalepsy was assessed using a wire grid fastened to a frame that wasinclined 60°.

2.3 DrugsD-amphetamine hemisulfate salt (Sigma-Aldrich, St. Louis, MO, USA), clozapine (Sigma-Aldrich), and PD149163 (NIMH Drug Repository, Bethesda, MD, USA) were dissolved in0.9% physiological saline. Haloperidol (Sigma-Aldrich) was dissolved in sterile water with afew drops of 85% lactic acid. All drugs were administered subcutaneously in a 1 ml/kgvolume 30 minutes prior to a test session.

2.4 CAR training and testingThe procedures used to assess CAR were similar to those reported previously from thislaboratory (Jacobson and Prus 2010). Briefly, rats were trained once daily in 15 minsessions, which consisted of approximately 15-25 trials (separated by randomly selectedintervals between 20 and 40 secs) depending on performance. Each trial began with an 80-dB white noise followed 10 sec later by electric shocks administered to the grid floor (0.6mA of 0.5 second duration, repeated every 1.5 sec). Moving to the opposite compartmentduring this 10 sec interval prevented onset of the shocks (avoidance response), whereasmoving to the opposite compartment after onset of the shocks terminated the shocks (escaperesponse). The white noise remained on until an animal emitted an avoidance or escaperesponse. If an escape response failed to occur after 60 secs (escape failure), the session wasterminated.

Test sessions were conducted after animals produced avoidance responses for at least 90%of training session trials for 3 consecutive sessions. Test sessions were 10 minutes long, butotherwise, identical to training sessions. Thirty minutes prior to a test session, a 10 minutepretest was conducted to determine if animals were performing accurately, andsubsequently, a rat was not tested that day if it failed to emit avoidance responses for 90% ofthe pre-test trials. Immediately following the pre-test session, drug or vehicle administrationwas given and a test session was conducted 30 minutes later.

Each rat was tested once with every dose. Test conditions were balanced so that every doseof a dose response curve, including vehicle, were assigned among the nine rats (one rat wasremoved from the study; see results below), evaluated on the same test day. Otherwise, thedose assignments varied randomly for each animal. Rats were first tested with haloperidol,followed by PD149163, clozapine, and amphetamine. Tests sessions for each dose or vehiclefor a drug were separated by at least 2 days. After a dose response curve for a drug wascompleted, rats were given at least 7 days off from experimental procedures before testswith the next drug were conducted.

2.5 CatalepsyImmediately preceding a CAR test session, catalepsy was evaluated using an inclined grid.Rats were gently placed on a wire grid and the time to completely remove one paw wasmeasured, excluding the first 30 seconds. Times were then scored according to the followingscale: 0=0-0.08; 1=0.09-0.35; 2=0.36-0.80; 3=0.81-1.42; 4=1.43-2.25; 5≥2.25 min(Ahlenius and Hillegaart 1986; Wadenberg et al. 2001).

Holly et al. Page 3

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

2.6 Data analysisPercent avoidance was calculated by dividing the number of trials where an avoidanceoccurred over the total number of trials for the session. Then, this value was multiplied by100. These percentage values were expressed as medians (+/- semi-interquartile range).

These and other data were analyzed using a Friedman one-way analysis of variance(ANOVA) by ranks, followed by the Wilcoxon matched-pairs signed ranks test, asappropriate, using GraphPad Prism v. 5.01 (GraphPad Software, Inc., La Jolla, California,USA).

3. Results3.1 CAR training

Of the 10 rats used in this study, one was removed from the study due to failure to maintaintraining criteria. The remaining nine rats were trained within a mean of 15.11 days (=/-standard error of the mean = 1.67 days).

3.2 Percent CARPercent CAR data are shown in figure 1.

PD149163 produced a significant reduction of CAR (χ2=36.67, DF=6, p<0.0001) (leftpanel). Percent avoidance at the 1.0 and 8.0 mg/kg doses was significantly lower thanvehicle. No escape failures occurred.

Clozapine also significantly reduced CAR (χ2=24.36, DF=3, p<0.0001), which was foundfor the 10.0 mg/kg dose versus vehicle control (center panel). No escape failures occurredfor clozapine.

Haloperidol produced a significant suppression of CAR (χ2=43.29, DF=6, p<0.0001), whichoccurred at the 0.1, 0.3, and 1.0 mg/kg doses compared to vehicle (right panel). Escapefailures occurred at the 0.05, 0.1, 0.3 and 1.0 mg/kg doses (data not shown).

No statistically significant effects on CAR were observed after amphetamine administration(data not shown).

3.3 CatalepsyCatalepsy scores are shown in Figure 2.

Neither PD149163 (left panel) nor clozapine (center panel) produced a statisticallysignificant increase in catalepsy scores. However, haloperidol produced a statisticallysignificant increase in catalepsy scores (χ2=28.91, DF=6, p<0.0001), which occurred at the1.0 mg/kg dose compared to vehicle (right panel).

No statistically significant effects on catalepsy were observed after amphetamineadministration (data not shown).

4. DiscussionIn the present study, PD149163 significantly decreased CAR without producing increases incatalepsy. These effects on CAR were observed at a 1.0 mg/kg dose, which has been shownto be an effective dose in many APD behavioral models in rats, including a reversal ofamphetamine-, MK801- (Feifel et al. 1999), DOI- (Feifel et al. 2003; Shilling et al. 2004),and cirazoline-induced (Shilling et al. 2004) prepulse inhibition deficits, of inherent prepulse

Holly et al. Page 4

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

deficits in Brattleboro rats (Feifel et al. 2004; Feifel et al. 2009), and of amphetamine-induced increases in locomotion (Feifel et al. 2008). Moreover, a 1.0 mg/kg dose ofPD149163 inhibited fear potentiated startle responses (Shilling and Feifel 2008), suggestingpotential anxiolytic effects. An inhibition of CAR, but no increase in catalepsy, was found atan 8.0 mg/kg dose, well beyond the behaviorally effective doses of PD149163 describedabove.

In the present study, the atypical APD clozapine produced full inhibition of CAR and failedto produce increases in catalepsy scores at up to a 10.0 mg/kg dose. Clozapine inhibition ofCAR has been demonstrated in numerous studies in rats using similar doses (Hertel et al.1999; Olsen et al. 2006; Wadenberg et al. 1998), and an inability to induce catalepsy hasbeen evaluated at much higher doses. For example, clozapine has failed to increase catalepsyvalues in rats at 15 mg/kg (Feifel et al. 2004), 17 mg/kg (Bartoszyk et al. 1996), and 40 mg/kg (Millan et al. 1998) doses. Furthermore, clozapine has been shown to prevent catalepsyinduced by a 1.0 mg/kg dose of haloperidol (Bartoszyk et al. 1996; Millan et al. 1998).Similar increases in catalepsy measures by haloperidol were found in the present study usinga 0.3 and 1.0 mg/kg dose, although a potential reversal of these effects by clozapine orPD149163 was not evaluated. However, the NT1 receptor agonist NT69L, which appears tohave a potency similar to PD149163 in several APD animal models (e.g., Boules et al. 2001;Cusack et al. 2000), is also without cataleptic effects. Further, NT69L has been shown toprevent catalepsy induced by a 1.0 mg/kg dose of haloperidol (Cusack et al. 2000).

While the inhibition of CAR by PD149163 is qualitatively similar to the effects found withclozapine and haloperidol, PD149163 did not produce the same magnitude of inhibition.Clozapine and haloperidol produced a median of 0% CAR at the highest doses tested, whilePD149163 only produced a median of approximately 50% and 60% CAR at the two highestdoses tested, 1.0 and 8.0 mg/kg, respectively. Although it is possible that still higher dosesof PD149163 may have achieved a greater inhibition of CAR, PD149163 was evaluated at adose (8.0 mg/kg) that was far higher than those demonstrated to be behaviorally effective inother APD models (discussed above). There was also not a trend toward greater CARinhibition between the 1.0 and 8.0 mg/kg doses.

However, the lack of further CAR inhibition does not appear unique to PD149163. The NT1receptor agonist NT69L, at a 0.32 mg/kg dose, produced a mean maximum inhibition ofCAR of approximately 50% (Hertel et al. 2001). Further, intracerebroventricularadministration of NT into the lateral ventricle, at amounts ranging from 0.2 – 17.0 nmoles,only reduced mean percent CAR to approximately 85%, and similar to the present findings,there was no discernable trend toward further inhibition beyond 0.6 nmoles (Luttinger et al.1982). PD149163 has also exhibited a varying degree of reversal of prepulse inhibitiondeficits in rats. PD149163, at doses up to 1.0 mg/kg, has been shown to fully reverseprepulse inhibition deficits produced by amphetamine, but only partially reverse prepulseinhibition deficits produced by MK-801 (Feifel et al. 1999). However, PD149163, againusing doses up to 1.0 mg/kg, has also fully reversed innate PPI deficits in Brattelboro rats,using Long Evans rats as controls (Feifel et al. 2009).

The lack of effect of PD149163 on escape failures is similar to the Luttinger et al. (1982)findings, described earlier, which failed to find escape failures by intracerebroventricaladministration of neurotensin. In a further comparison, systemic administration of NT69L(0.08-0.31 mg/kg) also did not induce escape failures during CAR testing (Hertel et al.2001). Whereas clozapine generally does not produce escape failures in this task (Olsen etal. 2006; Wadenberg et al. 1998), haloperidol did produce an increase in escape failures atdoses ranging from 0.05 to 1.0 mg/kg, replicating findings reported previously (e.g., Hertelet al. 2001).

Holly et al. Page 5

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Studies that have evaluated the neuropharmacological mechanisms that mediate suppressionof CAR are too numerous to cover here. However, in a comprehensive review on the utilityof CAR for APD screening, Wandenberg and Hicks (1999) concluded that inhibition ofCAR is mediated by the mesocorticolimbic dopamine pathway, and moreover, that theinhibition of CAR produced by “false positives” (e.g., LSD, morphine) might also be due toeffects on this pathway. NT closely interacts with dopamine along this and the nigrostriatalpathway. NT is released from dopamine neurons in these pathways, and NT1 receptors,which PD149163 is highly selective for (Petrie et al. 2004), are co-localized with D2receptors. Activation of NT1 receptors causes an allosteric inhibition of D2 receptor binding,which may mediate the APD-like effects of NT and NT receptor agonists (for review, seeBinder et al. 2001).

The present study provides further evidence for the putative atypical APD effects of the NT1receptor agonist PD149163, providing additional support for NT analogs as a novel class ofatypical APDs. While there is strong evidence for the mesocorticolimbic dopaminemediation of NT1 receptor agonist effects in APD models, the implications of closeinteractions between NT and other monoamines, for example serotonin (Jolas andAghajanian 1997), and a remaining controversy surrounding a possible tolerance to NT1receptor agonists after repeated administration (Elliott and Nemeroff 1986; Feifel et al.2010; Feifel et al. 2008; Hertel et al. 2001; Hertel et al. 2002), requires further evaluation ofthe utility of NT1 receptor agonists for the treatment of schizophrenia and possibly othermental disorders. Moreover, other properties of NT1 receptor agonists need to be assessed aswell. Importantly, neurotensin appears to enhance malignant pancreatic tumor growth, and isotherwise associated with breast, colorectal, lung, prostate, and various other cancers (forreview, see Mark Evers 2006). Thus, these and potential other limitations of neurotensinreceptor agonists must be addressed as the utility of these compounds for the treatment ofschizophrenia and other mental disorders are evaluated.

AcknowledgmentsThis study was funded by an NIMH grant to AJP (1R15MH083241-01). We are grateful for the technical assistanceof Stacie Davidson and Alexis Bench.

Role of Funding Source: Funding for this study was provided by NIMH Grant 1R15MH083241-01; the NIMH hadno further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; andin the decision to submit the paper for publication.

ReferencesAdams MR, Brandon EP, Chartoff EH, Idzerda RL, Dorsa DM, McKnight GS. Loss of haloperidol

induced gene expression and catalepsy in protein kinase A-deficient mice. Proc Natl Acad Sci U SA. 1997; 94:12157–61. [PubMed: 9342379]

Ahlenius S, Hillegaart V. Involvement of extrapyramidal motor mechanisms in the suppression oflocomotor activity by antipsychotic drugs: A comparison between the effects produced by pre- andpost-synaptic inhibition of dopaminergic neurotransmission. Pharmacology Biochemistry andBehavior. 1986; 24:1409–1415.

Bartoszyk GD, Roos C, Ziegler H. 5-HT1A receptors are not involved in clozapine's lack ofcataleptogenic potential. Neuropharmacology. 1996; 35:1645–6. [PubMed: 9025114]

Binder EB, Kinkead B, Owens MJ, Nemeroff CB. Neurotensin and dopamine interactions. PharmacolRev. 2001; 53:453–86. [PubMed: 11734615]

Boules M, Liang Y, Briody S, Miura T, Fauq I, Oliveros A, Wilson M, Khaniyev S, Williams K, Li Z,Qi Y, Katovich M, Richelson E. NT79: A novel neurotensin analog with selective behavioraleffects. Brain Res. 2010; 1308:35–46. [PubMed: 19874804]

Holly et al. Page 6

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Boules M, Warrington L, Fauq A, McCormick D, Richelson E. A novel neurotensin analog blockscocaine- and D-amphetamine-induced hyperactivity. Eur J Pharmacol. 2001; 426:73–6. [PubMed:11525773]

Cusack B, Boules M, Tyler BM, Fauq A, McCormick DJ, Richelson E. Effects of a novel neurotensinpeptide analog given extracranially on CNS behaviors mediated by apomorphine and haloperidol.Brain Res. 2000; 856:48–54. [PubMed: 10677610]

Elliott PJ, Nemeroff CB. Repeated neurotensin administration in the ventral tegmental area: effects onbaseline and D-amphetamine-induced locomotor activity. Neurosci Lett. 1986; 68:239–44.[PubMed: 3748452]

Feifel D, Goldenberg J, Melendez G, Shilling PD. The acute and subchronic effects of a brain-penetrating, neurotensin-1 receptor agonist on feeding, body weight and temperature.Neuropharmacology. 2010; 58:195–8. [PubMed: 19596358]

Feifel D, Melendez G, Murray RJ, Tina Tran DN, Rullan MA, Shilling PD. The reversal ofamphetamine-induced locomotor activation by a selective neurotensin-1 receptor agonist does notexhibit tolerance. Psychopharmacology (Berl). 2008; 200:197–203. [PubMed: 18568338]

Feifel D, Melendez G, Shilling PD. A systemically administered neurotensin agonist blocks disruptionof prepulse inhibition produced by a serotonin-2A agonist. Neuropsychopharmacology. 2003;28:651–3. [PubMed: 12655309]

Feifel D, Melendez G, Shilling PD. Reversal of sensorimotor gating deficits in Brattleboro rats byacute administration of clozapine and a neurotensin agonist, but not haloperidol: a potentialpredictive model for novel antipsychotic effects. Neuropsychopharmacology. 2004; 29:731–8.[PubMed: 14760394]

Feifel D, Mexal S, Melendez G, Liu PY, Goldenberg JR, Shilling PD. The brattleboro rat displays anatural deficit in social discrimination that is restored by clozapine and a neurotensin analog.Neuropsychopharmacology. 2009; 34:2011–8. [PubMed: 19322170]

Feifel D, Reza TL, Wustrow DJ, Davis MD. Novel antipsychotic-like effects on prepulse inhibition ofstartle produced by a neurotensin agonist. J Pharmacol Exp Ther. 1999; 288:710–3. [PubMed:9918579]

Gerlach J. Improving outcome in schizophrenia: the potential importance of EPS and neurolepticdysphoria. Ann Clin Psychiatry. 2002; 14:47–57. [PubMed: 12046640]

Goldstein JM. The new generation of antipsychotic drugs: how atypical are they? Int JNeuropsychopharmacol. 2000; 3:339–349. [PubMed: 11343614]

Hadden MK, Orwig KS, Kokko KP, Mazella J, Dix TA. Design, synthesis, and evaluation of theantipsychotic potential of orally bioavailable neurotensin (8-13) analogues containing non-naturalarginine and lysine residues. Neuropharmacology. 2005; 49:1149–59. [PubMed: 16095636]

Hertel P, Byskov L, Didriksen M, Arnt J. Induction of tolerance to the suppressant effect of theneurotensin analogue NT69L on amphetamine-induced hyperactivity. Eur J Pharmacol. 2001;422:77–81. [PubMed: 11430916]

Hertel P, Fagerquist MV, Svensson TH. Enhanced cortical dopamine output and antipsychotic-likeeffects of raclopride by alpha2 adrenoceptor blockade. Science. 1999; 286:105–7. [PubMed:10506554]

Hertel P, Olsen CK, Arnt J. Repeated administration of the neurotensin analogue NT69L inducestolerance to its suppressant effect on conditioned avoidance behaviour. Eur J Pharmacol. 2002;439:107–11. [PubMed: 11937099]

Jacobson SM, Prus AJ. Evaluation of the effects of alpha2 adrenoceptor antagonism with the D2receptor antagonist raclopride on conditioned avoidance responding in rats. Behav Pharmacol.2010; 21:654–9. [PubMed: 20729715]

Jolas T, Aghajanian GK. Neurotensin and the serotonergic system. Prog Neurobiol. 1997; 52:455–68.[PubMed: 9316156]

Luttinger D, Nemeroff CB, Prange AJ Jr. The effects of neuropeptides on discrete-trial conditionedavoidance responding. Brain Res. 1982; 237:183–92. [PubMed: 6176291]

Mark Evers B. Neurotensin and growth of normal and neoplastic tissues. Peptides. 2006; 27:2424–2433. [PubMed: 16904238]

Holly et al. Page 7

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Millan MJ, Schreiber R, Dekeyne A, Rivet JM, Bervoets K, Mavridis M, Sebban C, Maurel-Remy S,Newman-Tancredi A, Spedding M, Muller O, Lavielle G, Brocco M. S 16924 ((R)-2-{1-[2-(2,3-Dihydro-Benzo[1,4] Dioxin-5-Yloxy)-Ethyl]-Pyrrolidin-3yl}-1-(4-Fluoro-Phenyl)-Ethanone), aNovel, Potential Antipsychotic with Marked Serotonin (5-HT)1A Agonist Properties: II.Functional Profile in Comparison to Clozapine and Haloperidol. Journal of Pharmacology andExperimental Therapeutics. 1998; 286:1356–1373. [PubMed: 9732399]

National Research Council. Guide for laboratory animal facilities and care. National Research Council,National Research Council; 1996.

Olsen CK, Kreilgaard M, Didriksen M. Positive modulation of glutamatergic receptors potentiates thesuppressive effects of antipsychotics on conditioned avoidance responding in rats. PharmacolBiochem Behav. 2006; 84:259–65. [PubMed: 16782180]

Petrie KA, Bubser M, Casey CD, Davis MD, Roth BL, Deutch AY. The neurotensin agonistPD149163 increases Fos expression in the prefrontal cortex of the rat. Neuropsychopharmacology.2004; 29:1878–88. [PubMed: 15150532]

Sarhan S, Hitchcock JM, Grauffel CA, Wettstein JG. Comparative antipsychotic profiles ofneurotensin and a related systemically active peptide agonist. Peptides. 1997; 18:1223–7.[PubMed: 9396065]

Shibata K, Yamada K, Furukawa T. Possible neuronal mechanisms involved in neurotensin-inducedcatalepsy in mice. Psychopharmacology (Berl). 1987; 91:288–92. [PubMed: 2882538]

Shilling PD, Feifel D. The neurotensin-1 receptor agonist PD149163 blocks fear-potentiated startle.Pharmacol Biochem Behav. 2008; 90:748–52. [PubMed: 18577396]

Shilling PD, Melendez G, Priebe K, Richelson E, Feifel D. Neurotensin agonists block the prepulseinhibition deficits produced by a 5-HT2A and an alpha1 agonist. Psychopharmacology (Berl).2004; 175:353–9. [PubMed: 15107967]

Shilling PD, Richelson E, Feifel D. The effects of systemic NT69L, a neurotensin agonist, on baselineand drug-disrupted prepulse inhibition. Behav Brain Res. 2003; 143:7–14. [PubMed: 12842291]

Snijders R, Kramarcy NR, Hurd RW, Nemeroff CB, Dunn AJ. Neurotensin induces catalepsy in mice.Neuropharmacology. 1982; 21:465–8. [PubMed: 6810195]

Wadenberg MG, Browning JL, Young KA, Hicks PB. Antagonism at 5-HT(2A) receptors potentiatesthe effect of haloperidol in a conditioned avoidance response task in rats. Pharmacol BiochemBehav. 2001; 68:363–70. [PubMed: 11325387]

Wadenberg ML, Hicks PB. The conditioned avoidance response test re-evaluated: is it a sensitive testfor the detection of potentially atypical antipsychotics? Neurosci Biobehav Rev. 1999; 23:851–62.[PubMed: 10541060]

Wadenberg ML, Young KA, Trompler RA, Zavodny RA, Richter TJ, Hicks PB. A novel computer-controlled conditioned avoidance apparatus for rats. J Pharmacol Toxicol Methods. 1998; 38:211–5. [PubMed: 9566445]

Wustrow DJ, Davis MD, Akunne HC, Corbin AE, Wiley JN, Wise LD, Heffner TG. Reduced amidebond neurotensin 8-13 mimetics with potent in vivo activity. Bioorganic & Medicinal ChemistryLetters. 1995; 5:997–1002.

Holly et al. Page 8

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Figure 1.The effects of PD149163 (left), clozapine (center), and haloperidol (right) on medianpercent conditioned avoidance responding (+/- semi-interquartile range; N=9 for each drug).***p<0.001, **p<0.01, and *p<0.05 versus vehicle (VEH). N=9

Holly et al. Page 9

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

Figure 2.The effects of PD149163 (left), clozapine (center), and haloperidol (right) on mediancatalepsy scores (+/- semi-interquartile range; N=9 for each drug). ***p<0.001, **p<0.01,and *p<0.05 versus VEH

Holly et al. Page 10

Eur Neuropsychopharmacol. Author manuscript; available in PMC 2012 July 1.

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript

NIH

-PA Author Manuscript